Calender and an arrangement for fastening rolls of a calender

ABSTRACT

A calender and an arrangement for mounting calender rolls, the calender comprising at least two calender nips ( 1, 2 ) formed by at least two stacked rolls ( 11–14 ). The rolls are have bearing housings ( 3–6 ) by means of which the rolls ( 11–14 ) are stacked into roll pairs forming the calender nips ( 1, 2 ), and means ( 31, 32 ) connecting the bearing housings ( 3, 4  and  4, 5 ) of the rolls pairs with each other. At least two successive calender nips ( 1, 2 ) are arranged so that in the successive nips the mutual distance between the longitudinal axes of the lower rolls ( 12, 14 ) is smaller than the corresponding mutual distance between the respective upper rolls ( 11, 13 ) of the nips, whereby the disposition of the rolls ( 11–14 ) forms a V-shaped angle as seen from the end of the calender machinery and thus forms an operating area between the nips for changing the rolls. The rolls are combined into nips advantageously using heatable pull rods inserted through the bearing housings.

PRIORITY CLAIM

This is a national stage of PCT application No. PCT/FI00/00885, filed onOct. 10, 2000. Priority is claimed on that application and on patentapplication No. 19992214 filed in Finland on Oct. 13, 1999.

FIELD OF THE INVENTION

The present invention relates to a calender for surface-treating amoving web of paper or board.

The invention also relates to a construction suited for mutual mountingof calender rolls.

BACKGROUND OF THE INVENTION

Different types of calenders are used for improving the smoothness andsurface profile of manufactured sheet of paper or board. One of theconcurrent calender types is the soft-nip calender comprising at leasttwo calender nips operating in succession along the sheet travel,whereby each nip is formed by a soft roll and a hard roll mounted torotate on each other. Today, the soft roll is generally surfaced with apolymer coating, while the hard roll is a heatable roll made from castiron. The different types of rolls are mounted as an alternatingsuccession in a vertical stack thus forming successive nips, wherebyeither side of a running web travels alternately over a soft roll, ahard roll and so on, thus making both sides of the sheet maximally equalafter the surface-treatment. The calender rolls, particularly the softroll, undergo wear during the use, thereby invoking a need of scheduledreplacement. Today, two different techniques of roll replacement areused. In one arrangement, the old roll with its bearing housings iselevated away from its operating position by means of an overhead hoist.Herein, either the upper roll must always be removed before the lowerroll can be replaced or, alternatively, the roll stacks must be askewedfrom a vertical plane in order to facilitate a sideways obliquelyperformed lifting of the lower roll away from its normal position underthe upper roll. Also in vertically aligned roll stacks it is possible toimplement the removal of the lower roll to take place in a sidewaysdirection by first shifting the lower roll laterally away from under theupper roll. In this type of a construction, the frame of the calenderstack must be open at least in the direction of the lower roll removal.

When the construction is such as to allow the lower roll to be removedonly after the removal of the upper roll, the roll replacement operationbecomes extremely clumsy, particularly if the upper roll is a heatableroll, as is the case inevitably always for the second nip, because theroll connections such as those of the heating medium circulation must bedisconnected during the removal of the roll. In a roll replacementsystem with a sideways shifting arrangement of the rolls, sufficientfree space must be reserved for the movement of either roll. Suchservicing space for roll replacement requires more footprint about thecalender. As the roll diameters in modern papermaking machines arelarge, the headroom for roll replacement may be as large as two metersper roll and, since a calender always has at least two calender nips,the need of lateral footprint may be up to four meters for a two-nipcalender. Obviously, this kind of roll mounting is not possible in suchmachinery rebuild operations wherein a soft-nip calender must be fittedto replace an outdated machine calender. During machinery rebuild, itmay be necessary to relocate various units of the papermaking machineryand increase the length of the machine, which is expensive. Also in newfactory projects, a machine of a larger overall length increases costsdue to larger footprint, among other factors. Another drawback of alarge lateral roll change space is that the web must travel as open drawover the roll change space, because this portion of machinery cannot beequipped with auxiliary devices. Long, open web draws increase the riskof web breaks and complicate web tail threading.

It is also possible to replace the lower roll of a calendar nip by wayof elevating the upper roll apart from the lower roll and then movingthe lower roll with its bearing housings aside supported by a rolltransfer carriage, whereupon the roll can be replaced. This arrangementis hampered by the large lateral space required about the roll and itsneed for a dual set of roll handling equipment, whereby the lift must becomplemented with at least two transfer carriages, which makes thisconstruction costly.

Attempts have been made to reduce the space requirement of the calenderin the machine direction of the web travel by way of, e.g., locating thecalender frames of two successive roll nips, the frames having one openside, in a back-to-back disposition of the frames by their closed sides,whereby the web travel between the successive nips is maximallyminimized. While this arrangement needs a smaller layout footprint, aproblem arises from the roll replacement operations that now must beperformed on opposite sides of the calender frame thus still needing asmuch roll change headroom as in any other conventional calender.

SUMMARY OF THE INVENTION

Other objects and features of the present invention will become apparentfrom the following detailed description considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are intended solely for purposes of illustration and not as adefinition of the limits of the invention, for which reference should bemade to the appended claims.

It is an object of the present invention to provide an entirely noveltype of calender construction capable of overcoming the problems of theprior art techniques described above.

The goal of the invention is achieved by way of disposing two successivecalender nips so that the mutual distance between the lower rolls of thesuccessive nips is smaller than the mutual distance between the upperrolls of the nips, whereby the rolls of the nips as seen from their endsare disposed in a V-shaped configuration.

Herein, the calender rolls can be connected to each other by means ofpull rods adapted to connect the roll bearing housings to each other,whereby the connections to the auxiliary devices of the roll may beadapted into the roll stack so as form an integrated auxiliary equipmentassembly.

The invention offers significant benefits.

By virtue of the invention, it is possible to gain a substantialreduction in the footprint occupied in the machine direction by acalender such as a soft-nip calender or the like comprising a pluralityof separate roll nips.

The invention also facilitates a simple replacement of the lower rolls.The calender framework becomes extremely uncomplicated and lightweight,because the roll bearing housings are connected to each other so thatthe nip forces are not transmitted to the framework. Now, since thecalender framework is relieved from high forces imposed thereon by theroll nips, also the calender foundations are not subjected to highstresses. Hence, a calender according to the invention is aptly suitedfor machine rebuilds intended, e.g., to improve the quality of themanufactured product with the help of a more efficient calender. Acalender according to the invention may even be fitted to replace asingle-stack machine calender in places where prior-art calenderconstructions could not necessarily be squeezed onto the footprint leftfree by a dismantled two-stack machine calender. Furthermore, the lengthof open web draws remains short and the number of guide rolls is smallerthan in conventional calender constructions. The bearing housings of anyroll pair forming a nip are connected to each other by techniques thatin an uncomplicated and precise manner give the required roll fixingforce also for the upper rolls, and there are provided transfer andsupport means for the auxiliary devices operating between the calendernips so as to permit the displacement of these devices for the time thelower rolls are being replaced. The fluid, electrical and otherconnections of the rolls and their auxiliary means are concentrated atthe roll ends and enclosed therein, whereby the connections have enoughheadroom so that there is no need to disconnect them from the rollsbeing replaced. It is even possible to design the entire calender intoan integrated unit that can be shipped to a customer and rapidly mountedon site as a replacement of an existing calender or as a part of newmachinery being erected.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be examined with the help ofexemplifying embodiments and by making reference to the appendeddrawings in which

FIG. 1 shows a conventional calender construction;

FIG. 2 shows another conventional calender construction;

FIG. 3 shows a third conventional calender construction;

FIG. 4 shows schematically an embodiment of the calender constructionaccording to the invention;

FIG. 5 shows schematically the roll replacement operation in thecalender embodiment of FIG. 4;

FIG. 6 shows schematically the roll replacement operation in thecalender embodiment of FIG. 4 when the lower roll is already removed;

FIG. 7 shows in a side view one mounting technique of calender bearinghousings;

FIG. 8 shows in a top view the arrangement of FIG. 7; and

FIG. 9 shows another mounting technique of calender bearing housings.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Referring to FIG. 1, the calender construction shown therein has bearinghousings 3–6 of rolls 11–14 connected to each other and the roll nips 1and 2 have separate frames. A web 15 enters a first roll nip, e.g., froman unwinder 9 and then travels from first a nip 1 to a second nip 2 overa guide/spreading roll 8. Next downstream from the calender is located aset of measurement equipment 10 and guide rolls that pass the web 15 tothe subsequent treatment stage such as a winder. Under each one of thebearing housings 3, 6 of the lower roll 12, 14 of either roll nip 1, 2is disposed a roll change carriage 7, and the roll change is performedby way of first detaching the bearing housings 3, 4 and 5, 6,respectively, from each other, then elevating the upper bearing housingupward and lowering the lower bearing housing onto the roll changecarriage 7 and subsequently moving the same clear from below the upperroll, thus allowing the roll to be changed at the side of the calender.In this exemplifying case, the machine-direction length of the calenderis 8300 mm, which can hardly be made shorter, because guide or spreadingrolls are necessarily needed between the calender nips 1, 2, as well asin front of them and after them.

In the embodiment of FIG. 2, C-shaped frames 16, 17 of the calender nips1, 2, respectively, are disposed back-to-back, and the bearing housings3, 6 of the lower rolls 12, 14, respectively, are mounted supported onhydraulic cylinders 18, thus allowing the housings during the rollchange operation to be lowered downward and then moved out of way pastthe frames 16, 17. Inasmuch the rolls 12, 14 may have a very largediameter, the operating space on both sides of the frame must be madewide, up to 2 m, in order to perform an unobstructed lift of thecalender rolls. Not even this arrangement can make the calendermachine-direction length shorter than the referenced dimension of 8400mm. Furthermore, the nip forces are imposed on the open frame of theroll nips that accordingly must be made very rigid and massive.

In the embodiment of FIG. 3, the frames 19, 20 are oriented in the samedirection. This arrangement is the most wasteful in terms of footprintusage and, consequently, in many cases the most expensive to implementgiving a reference dimension of 9700 mm for the length of this type ofcalender that, as is evident from the diagram, can hardly be madeshorter. It must be noted herein that, since the reference dimensionsgiven above represent those of the exemplifying embodiments, actuallyrequired operating space is ultimately determined by the basicdimensions of the machinery such as roll diameters.

In FIG. 4 is shown a schematic view of an embodiment according to theinvention. In this construction, the bearing housings 3–6 of thecalender rolls 11–14 are mounted on lightweight frames 21, 22.Additionally, the bearing housings 3–6 are connected to each other sothat the nip forces are not transmitted to the frames 21, 22 of thecalender nips 1, 2. The rolls 11, 12 and 13, 14 of either calender nip1, 2, respectively, are arranged in a mutually laterally displacedposition so that the longitudinal axes of the stacked rolls are notlocated in the same vertical plane. The calender frames 21, 22 areadapted in a facing disposition so that the mutual distance between thelongitudinal axes of the lower rolls of the roll nips is smaller thanthe corresponding mutual distance between the upper rolls of the nips,whereby the disposition of the rolls form a V-shaped angle as seen fromthe end of the calender machinery. This disposition allows the operatingarea for changing the lower rolls to be adapted between the opposedcalender nips 1, 2 thus disposing with the need for two separate rollchange areas. In the illustrated exemplifying embodiment, each calendernip comprises a soft roll 11, 14 and a heatable hard roll 12, 13 thatforms a nip with its respective soft roll.

For changing the rolls, the calender according to the invention iscomplemented with some auxiliary means. The bearing housings 4, 5 of theupper rolls 11, 13 are mounted on guides 24 which are fixed to theframes 21 and 22 and along which the bearing housings can be slidablyelevated upward away from their superimposed location above the bearinghousings 3, 6 of the lower rolls 12, 14. Obviously, the guides 24 may bereplaced by any other similar guidance means. The intervening unitsbetween the calender nips, such as rolls, a steam box, measurementequipment or other possible auxiliary devices can be advantageouslycombined into an integrated assembly 23 that is mounted to the upperroll bearing housing 5 by aligning the assembly with a keyed connectionand then fixing it in place by means of bolts. Alternatively, theassembly with its auxiliary devices can be mounted on the lower rollbearing housing. In the exemplifying embodiment shown in FIGS. 4 and 5,the assembly includes only one roll. Obviously, the assembly can beintegrated to include any necessary auxiliary devices with theirelectrical, fluid and compressed-air connections so dimensioned that theassembly can be lowered below the lower rolls, between the calendernips, for the duration of a roll change. The integrated auxiliaryequipment assembly 23 can be lowered to rest on fixing means adapted tothe calender frame 22 as shown in FIG. 4 or, alternatively, onto thefloor as shown in FIG. 5.

In this calender embodiment, the change of the upper rolls 11, 13 can bemade simply by using a lift for elevating the roll away from itsoperating position above the lower roll bearing housing. The lower rolls12, 14 are changed by way of disconnecting the bearing housings fromeach other and then lifting the upper rolls 11, 13 upward along theguides 24. Next, the bearing housings 3, 6 of the lower rolls 12, 14 aredetached from the frames 21, 22, whereupon the rolls can be transferredby a lift away from the lift area remaining between the calender nips 1,2. Prior to the lifting of the lower rolls and, advantageously, beforethe bearing housings are detached, the auxiliary equipment assembly 23is detached and lowered down to keep it clear from the transfer path ofthe lower rolls. Obviously, the installation of a new roll takes placein a reverse order. To assure fast roll replacement, it is essential tohave the connections of the upper rolls 11, 13 and the auxiliaryequipment assembly 23 implemented with such dimensioning rules thatthese units need not be dismantled when these units must be moved aside.

In FIG. 6 are shown the details related to the roll change operation andthe construction of the calender frame and its bearing housings. Herein,the frame 22 has a box-section structure in which the waist plates ofthe frame form a U-section in which the sides act as guide surfaces 24for the movement of the upper bearing housing 5. In the diagram, theupper bearing housing 5 is shown elevated into its upper position forthe duration of the roll change. The bearing housing 5 is supported tothe frame 22 by means of a pin 36 fitted into a hole made to the frame.

The lower roll is replaced as follows. First, the auxiliary equipmentassembly 23 situated in front of the nip is detached from the bearinghousings 5, 6 and is lowered below the lower roll without any need todismantle its connections, whereupon the bearing housings 5, 6 can bedisconnected from each other. The upper roll is elevated upward underthe guidance provided by the guide surfaces 24 formed on the frame 22and is locked in place by way of, e.g., pushing a pin 36 either manuallyor by actuator means through the holes made to the upper part of theframe 22 and the upper part of the bearing housing 5. Resultingly, theupper roll remains resting on the pin supported by the bearing housing 5so that the lower edge of the bearing housing 5 leans against the frame22. The connections of the upper roll must be designed such that theypermit lifting the roll into its locked position during roll changewithout any need for dismantling the connections. Hereafter, the lowerroll bearing housings 6, as well as the connections of the roll and themechanical drive shaft thereof, are detached from the frame 22. If thereare any auxiliary devices located in front of the lower roll, such as acleaning doctor, the auxiliary devices are rotated aside clear of theroll change transfer path either manually or using powered actuators.Subsequently, the lower roll with its bearing housings 6 can be elevatedaway from the area remaining between the roll nips. Obviously, theinstallation of a new roll takes place in a reverse order.

As mentioned earlier, the present invention relates to calenderconstructions in which the bearing housings of the calender rolls areconnected to each other. The required nip force as well as the openingand closing of the nip are implemented by means of a mechanism acting ona deflection-compensated roll; whereby the calender frame receives onlya minimal portion of the reactive forces resulting from the actuation ofthe nip pressure. To achieve a fast and reliable roll change and, aboveall, easy installation of a new roll, the connection of bearing housingsto each other must be designed to be uncomplicated and such that itgives a sufficiently large and very accurately correct nip force.Obviously, the embodiment must also assure an accurate alignment of thebearing housings.

In FIGS. 7 and 8 is shown one method for a reliable connection of thebearing housings 3, 4 to each other. In this embodiment, the bearinghousings are provided with planar or wedge-shaped clamping surfaces 27,whereby the bearing housings can be clamped together against each otherby means of clamp members 25 that are in a compatible manner providedwith wedge-shaped or planar surfaces 28. The clamp members are C-shapedand have their clamping surfaces on the inner sides of the shapedmember. The wedged contact between the clamping surfaces 27 of the clampmember and the respective projections of the bearing housings can beimplemented by way of using a wedged shape on both or only one of theopposed clamping surfaces. The clamp members 25 are made so wide as toextend over the entire width of the bearing housings, whereby they arepressed against the sides of the bearing housings by means of tensioningbolts 26 that connect the clamp members located on the opposite sides ofthe bearing housings to each other and thus press the clamp members 25against the side surfaces 27 of the clamping projections of the bearinghousings. In the illustrated embodiment, the tensioning bolts 26 aredisposed at the sides of the bearing housings and to ease theirinsertion, the upper bearing housing 4 is provided with bolt supportguides 29 through which the bolts are passed. When the tensioning boltsare tightened with a given torque, the bearing housings are compressedagainst each other at a given force. This mounting method is fast andreliable, yet needing less space in the machine direction than aconventional mounting technique using bolts. The illustrated mountingmethod permits an extremely rapid roll replacement in the calenderaccording to the invention and, hence, this mounting arrangement is alsoadvantageously used for connecting the lower bearing housing 3 to thecalender frame.

In FIG. 9 is shown an alternative method of mounting the bearinghousings 3, 4. Herein, into mounting holes 35 drilled to the bearinghousings 3, 4 are inserted pull rods 30, each of them having anelectrical heater element 34 removably or fixedly adapted into itscenter bore. The lower end of the pull rod has a collar projection 31adapted to rest against the edge of the mounting hole 35 drilled to thelower bearing housing 3. The upper end of the pull rod 30 has an annularrecess 33 capable of accommodating a locking piece 32 that rests againstthe edge of the mounting hole 35 drilled to the upper bearing housing 4.Obviously, the pull rod 30 may also be inserted into an invertedposition. Now, the mounting of the bearing housings takes place by wayof inserting the pull rods 30, after they are heated with the help ofthe heater elements 34, into the mounting holes 35 drilled to thesuperimposed bearing housings 3, 4, whereby the distance from theproximal edge of the collar projection 31 to the distal edge of theannular recess 33 is thermally extended so much that the locking piececan be inserted between the edge of the mounting hole 35 drilled to theupper bearing housing 4 and the distal edge of the annular recess 33. Inother words, the distance from the proximal edge of the locking piece tothe proximal edge of the pull rod collar projection at the beginning ofthe mounting operation is kept larger than the distance between theouter surfaces of the mounting holes 35 drilled to the bearing housings3, 4. The locking piece 32 may be, e.g., a split ring that is joinedwith bolts or as well any other conventional locking member. After thelocking piece 32 is firmly mounted in the annular recess 33, the heaterelement 34 is deenergized or pulled out from the pull rod center bore,whereupon the rod begins to contract thus pulling the bearing housingsagainst each other. At the ambient temperature of the calender, thetarget length of the contracted pull rod defined as the distance betweenthe proximal edges of its locking parts must be shorter than thedistance between the outer edge surfaces of the mounting holes drilledto accommodate the pull rods. Under very warm conditions, the ambienttemperature may rise as high as 40 to 50° C., while in the machineryhalls of cold-climate factories the ambient temperature can be veryclose to 0° C. Generally, the operating ambient temperature is in theorder of 10–30° C.

The connecting force imposed by the pull rods is easy to control to adesired value inasmuch the force generated by a contracting rod can bereadily computed. The pull rod is advantageously made from steel whosethermal expansion coefficient is known precisely. Obviously, the rod maybe made from any other material of a sufficiently high strength, wherebythe above-mentioned locking members 31, 32, 33 can be replaced by nutshaving a thread compatible with those made to the rod ends or,alternatively, other locking means can be used capable of accuratelypositioning the rod in its longitudinal axis direction. Instead of usinga heater element, the rod may be heated by other methods such as an ovenor a heating bath, but this technique requires a rapid installationsequence during which the rod may not cool down. The electrical heaterelement can be mounted in a permanent or removable manner.

In addition to the exemplifying embodiments described above, differentmodifications may be contemplated without departing from the spirit ofthe invention. While only a soft-nip calender is discussed above as anexample of calender types, the invention can as well be applied to allsuch calenders that include at least two calender nips formed by tworolls. The angle between the inclined roll stacks, that is, the V-angleddisposition between the adjacent roll stacks can be varied, however, notmaking the angle smaller that what is necessary to ensure unobstructedremoval of the lower roll from below the upper roll. The required tiltangle between the rolls stacks is determined by such factors as theouter dimensions of the rolls and their bearing housings. Typically, aline drawn through the centers of the upper roll and the lower roll isinclined by 15° in regard to the vertical plane. The number of calendernips may be greater than two, whereby each two calender nip pairs needstwo roll change spaces and so upward according to the increasing numberof calender nips. The number of rolls in a single assembly of nips mayalso be larger, whereby a typical arrangement is to use three rolls in astack. The bearing housings of the calender may be mounted using fixingmeans different from those described above.

The pull rod arrangement according to the invention is also applicableto single-nip calenders. These types of calenders include, e.g.,low-gloss calenders and machine calenders, wherein the peripheraldevices of the roll are advantageously integrated into an auxiliaryequipment assembly in the manner described above.

Thus, while there have been shown and described and pointed outfundamental novel features of the present invention as applied to apreferred embodiment thereof, it will be understood that variousomissions and substitutions and changes in the form and details of thedevices described and illustrated, and in their operation, and of themethods described may be made by those skilled in the art withoutdeparting from the spirit of the present invention. For example, it isexpressly intended that all combinations of those elements and/or methodsteps which perform substantially the same function in substantially thesame way to achieve the same results are within the scope of theinvention. Substitutions of elements from one described embodiment toanother are also fully intended and contemplated. It is also to beunderstood that the drawings are not necessarily drawn to scale but thatthey are merely conceptual in nature. It is the intention, therefore, tobe limited only as indicated by the scope of the claims appended hereto.

1. A calender comprising: at least two successive calender nips eachformed by at least two stacked rolls, wherein the calender nips arearranged so that a mutual distance between the longitudinal axes oflower rolls is smaller than a corresponding mutual distance betweenrespective upper rolls of the nips, so that the axes of the rolls asseen from the end of the rolls forms a V-shaped angle, thereby formingan operating area between the nips for changing the rolls; bearinghousings by means of which the rolls are mounted and stacked into rollpairs forming the calender nips; and means for fixedly connecting thebearing housings of each of the roll pairs to each other in pairs. 2.The calender of claim 1, wherein each one of the calender nips has atleast one soft roll and at least one heatable hard roll.
 3. The calenderof claim 1, further comprising at least two frames on which said bearinghousings of said rolls are mounted, and means mounted on at least one ofsaid frames for, during a change of one of the lower rolls, supportingthe bearing housings of the respective upper roll at a level higher thantheir normal operating position.
 4. The calender of claim 1, whereinconnections from at least the upper rolls to electrical, fluid,compressed air and other systems are so dimensioned that the upper rollscan be moved vertically without a need for dismantling the connectionsby a distance required for a change of the lower roll.
 5. The calenderof claim 3, wherein connections from at least the upper rolls toelectrical, fluid, compressed air and other systems are so dimensionedthat the upper rolls can be moved vertically without a need fordismantling the connections by a distance required for a change of thelower roll.
 6. The calender of claim 4, further comprising anintervening unit positioned between the calender nips and comprising atleast one of a roll, a measurement equipment, and another web handlingdevice, the intervening unit being positioned in a space where a roll ismoved when a roll is changed, the intervening unit being mounted on thecalender frame in a detachable manner and having connections theretodimensioned so that the intervening unit can be lowered below the levelof the lower rolls without dismantling connections to the interveningunit.
 7. The calender of claim 5, further comprising an intervening unitpositioned between the calender nips and comprising at least one of aroll, a measurement equipment, and another web handling device, theintervening unit being positioned in a space where a roll is moved whena roll is changed, the intervening unit being mounted on the calenderframe in a detachable manner and having connections thereto dimensionedso that the intervening unit can be lowered below the level of the lowerrolls without dismantling connections to the intervening unit.
 8. Thecalender of claim 1, wherein said means for fixedly connecting saidbearing housings comprises pull rods having locking means adaptedthereon so that at an operating temperature a distance between proximaledges of said locking means is shorter than the distance between outeredge surfaces of mounting holes formed in two superimposed bearinghousings, and so that when said pull rods are heated the distancebetween said proximal edges of said locking means becomes larger thansaid distance between said outer edge surfaces of said mounting holes.9. The calender of claim 8, wherein a bore is formed in the pull rod soas to accommodate therein a heater element.
 10. The calender of claim 9,further comprising a heater element mounted in the bore of the pull rod.11. The calender of claim 10, wherein the heater element is removablymounted in the bore of the pull rod.
 12. The calender of claim 10,wherein the heater element is fixedly mounted in the bore of the pullrod.
 13. The calender of claim 1, wherein said means for fixedlyconnecting said bearing housings comprises at least two clamp pieceshaving two clamping surfaces that are in an opposed disposition and arespaced apart from one another, wherein said bearing housings have twopairs of compatible clamping surfaces on external sides spaced apartfrom each other, said two pairs of compatible clamping surfaces beingoriented outwardly relative to each other and being shaped to formwedge-shaped mating surfaces in combination with said clamping surfacesof said clamp pieces, said means for fixedly connecting said bearinghousings further comprising at least one bolt for compressing said clamppieces onto said clamping surfaces of said bearing housings.
 14. Thecalender of claim 8, further comprising an intervening unit positionedbetween the calender nips and comprising at least one of a roll, ameasurement equipment, and another web handling device, the interveningunit being positioned in a space where a roll is moved when a roll ischanged, the intervening unit being mounted on the calender frame in adetachable manner and having connections thereto dimensioned so that theintervening unit can be lowered below the level of the lower rollswithout dismantling connections to the intervening unit.
 15. Thecalender of claim 9, further comprising an intervening unit positionedbetween the calender nips and comprising at least one of a roll, ameasurement equipment, and another web handling device, the interveningunit being positioned in a space where a roll is moved when a roll ischanged, the intervening unit being mounted on the calender frame in adetachable manner and having connections thereto dimensioned so that theintervening unit can be lowered below the level of the lower rollswithout dismantling connections to the intervening unit.
 16. A calendercomprising: at least two successive calender nips each formed by atleast two stacked rolls, wherein the calender nips are arranged so thata mutual distance between the longitudinal axes of lower rolls issmaller than a corresponding mutual distance between respective upperrolls of the nips, so that the axes of the rolls as seen from the end ofthe rolls forms a V-shaped angle, thereby forming an operating areabetween the nips for changing the rolls; bearing housings by means ofwhich the rolls are stacked into roll pairs forming the calender nips;means for mounting the bearing housings of the rolls pairs to eachother, wherein connections from at least the upper rolls to electrical,fluid, compressed air and other systems are so dimensioned that theupper rolls can be moved vertically without a need for dismantling theconnections by a distance required for a change of the lower roll; andan intervening unit positioned between the calender nips and comprisingat least one of a roll, a measurement equipment, and another webhandling device, the intervening unit being positioned in a space wherea roll is moved when a roll is changed, the intervening unit beingmounted on the calender frame in a detachable manner and havingconnections thereto dimensioned so that the intervening unit can belowered below the level of the lower rolls without dismantlingconnections to the intervening unit.
 17. A calender comprising: at leasttwo successive calender nips each formed by at least two stacked rolls,wherein the calender nips are arranged so that a mutual distance betweenthe longitudinal axes of lower rolls is smaller than a correspondingmutual distance between respective upper rolls of the nips, so that theaxes of the rolls as seen from the end of the rolls forms a V-shapedangle, thereby forming an operating area between the nips for changingthe rolls; bearing housings by means of which the rolls are stacked intoroll pairs forming the calender nips; means for mounting the bearinghousings of the rolls pairs to each other; at least two frames on whichsaid bearing housings of said rolls are mounted, and means mounted on atleast one of said frames for, during a change of one of the lower rolls,supporting the bearing housings of the respective upper roll at a levelhigher than their normal operating position, wherein connections from atleast the upper rolls to electrical, fluid, compressed air and othersystems are so dimensioned that the upper rolls can be moved verticallywithout a need for dismantling the connections by a distance requiredfor a change of the lower roll; and an intervening unit positionedbetween the calender nips and comprising at least one of a roll, ameasurement equipment, and another web handling device, the interveningunit being positioned in a space where a roll is moved when a roll ischanged, the intervening unit being mounted on the calender frame in adetachable manner and having connections thereto dimensioned so that theintervening unit can be lowered below the level of the lower rollswithout dismantling connections to the intervening unit.
 18. A calendercomprising: at least two successive calender nips each formed by atleast two stacked rolls, wherein the calender nips are arranged so thata mutual distance between the longitudinal axes of lower rolls issmaller than a corresponding mutual distance between respective upperrolls of the nips, so that the axes of the rolls as seen from the end ofthe rolls forms a V-shaped angle, thereby forming an operating areabetween the nips for changing the rolls; bearing housings by means ofwhich the rolls are stacked into roll pairs forming the calender nips;means for mounting the bearing housings of the rolls pairs to eachother, wherein said means for mounting said bearing housings comprisespull rods having locking means adapted thereon so that at an operatingtemperature a distance between proximal edges of said locking means isshorter than the distance between outer edge surfaces of mounting holesformed in two superimposed bearing housings, and so that when said pullrods are heated the distance between said proximal edges of said lockingmeans becomes larger than said distance between said outer edge surfacesof said mounting holes.
 19. The calender of claim 18, wherein a bore isformed in the pull rod so as to accommodate therein a heater element.20. The calender of claim 19, further comprising a heater elementmounted in the bore of the pull rod.
 21. The calender of claim 18,further comprising an intervening unit positioned between the calendernips and comprising at least one of a roll, a measurement equipment, andanother web handling device, the intervening unit being positioned in aspace where a roll is moved when a roll is changed, the intervening unitbeing mounted on the calender frame in a detachable manner and havingconnections thereto dimensioned so that the intervening unit can belowered below the level of the lower rolls without dismantlingconnections to the intervening unit.
 22. The calender of claim 19,further comprising an intervening unit positioned between the calendernips and comprising at least one of a roll, a measurement equipment, andanother web handling device, the intervening unit being positioned in aspace where a roll is moved when a roll is changed, the intervening unitbeing mounted on the calender frame in a detachable manner and havingconnections thereto dimensioned so that the intervening unit can belowered below the level of the lower rolls without dismantlingconnections to the intervening unit.
 23. The calender of claim 20,wherein the heater element is removably mounted in the bore of the pullrod.
 24. The calender of claim 20, wherein the heater element is fixedlymounted in the bore of the pull rod.
 25. The calender of claim 18,wherein said means for mounting said bearing housings comprises at leasttwo clamp pieces having two clamping surfaces that are in an opposeddisposition and are spaced apart from one another, wherein said bearinghousings have two pairs of compatible clamping surfaces on externalsides spaced apart from each other, said two pairs of compatibleclamping surfaces being oriented outwardly relative to each other andbeing shaped to form wedge-shaped mating surfaces in combination withsaid clamping surfaces of said clamp pieces, said means for mountingsaid bearing housings further comprising at least one bolt forcompressing said clamp pieces onto said clamping surfaces of saidbearing housings.